A highly proton conductive perfluorinated covalent triazine framework via low-temperature synthesis

Proton-conducting materials are essential to the emerging hydrogen economy. Covalent triazine frameworks (CTFs) are promising proton-conducting materials at high temperatures but need more effective sites to strengthen interaction for proton carriers. However, their construction and design in a concise condition are still challenges. Herein, we show a low temperature approach to synthesize CTFs via a direct cyclotrimerization of aromatic aldehyde using ammonium iodide as facile nitrogen source. Among the CTFs, the perfluorinated CTF (CTF-TF) was successfully synthesized with much lower temperature ( ≤ 160 °C) and open-air atmosphere. Due to the additional hydrogen-bonding interaction between fluorine atoms and proton carriers (H3PO4), the CTF-TF achieves a proton conductivity of 1.82 × 10−1 S cm−1 at 150 °C after H3PO4 loading. Moreover, the CTF-TF can be readily integrated into mixed matrix membranes, displaying high proton conduction abilities and good mechanical strength. This work provides an alternative strategy for rational design of proton conducting media.

5 The optimum conditions for the synthesis of CTFs are not given.The yield provided in the text should be specified for some reaction temperature.All the yield results should be provided for every reaction temperatures.
6 The so-called host-guest interaction in CTFs, the authors should provide some more convinced evidence, experimental or theoretical results.
7 Some typo and grammar errors should be corrected.The following are some examples.
the frameworks with more strengthened anchoring sites is (are) preferred 130 ppm ~145 ppm (130 ~145 ppm) "Scanning electron microscope (SEM) and transmission electron microscope (TEM) were employed to observe the microscopic morphology" Only the SEM results are employed to observe the morphology.
The proton conducting materials possessing good processability and flexibility is (are) desired.
The research of porous organic polymers in the field of proton conduction are (is) mostly focused on powder form interreact (interact) with H3PO4 [1] The authors should compare the fluorine content of their CTF-TF with other CTFs that have been prepared by different methods and reported in the references.This would show how effective their synthesis method is for introducing fluorine atoms into the CTFs.
Response: Thank you for your insightful comments.Following your suggestion, we listed the fluorinated CTFs reported previously and made the detailed comparison, which shows the clear advantages of our method (see Supplementary Table 1).From this Table, the advantages of this work in synthesizing perfluorinated CTFs are illustrated from the following aspects: Firstly, we compared the fluorine content of CTF-TF with the CTFs reported in references.
It shows that the fluorine content in our method is higher than most reported CTFs synthesized by ionothermal method at high temperatures (>400 ℃), due to the cleavage of C-F bond at high temperatures (>400 ℃).There is only one case with fluorine content of 23.8 wt% for fluorinated CTFs via conventional ionothermal method at high temperatures (>400 ℃) (Energy Environ. Sci. 2013, 6, 3684-3692), and the fluorine contents of most reported CTFs are lesser than 15 wt% (Chem.Eng.J. 2020, 400. 125967;Sep. Purif. Technol. 2022, 290, 120857).While, in the fluorinated CTF obtained by strong acid catalysis, the fluorine content was not explicitly 2 / 37 disclosed (J.Am.Chem. Soc. 2020, 142, 6856-6860), where the synthesis is still conducted under high temperatures (250-350 ℃) and particularly the surface area is only 2 m 2 g -1 , much lower than that of CTF-TF in our work (407.7 m 2 g -1 ), which is not preferable to accommodate more proton carriers.
Secondly, to achieve excellent proton conductivity, it is important to retain intact of the chemical structure during synthesis and high content of the hydrogen bond acceptors in the framework, so it is highly preferable to synthesize the materials at mild conditions.To achieve fluorinated CTFs with higher fluorine content, the researchers have struggled to developed new methods to synthesize them at lower temperatures.Although an improved ionothermal method to synthesize a perfluorinated CTF at relatively lower temperatures has been reported (Angew. Chem.Int. Ed. 2021, 60, 25688-2569), which exhibits a fluorine content (31wt%) comparable to that of ) in this work, the operation of synthesis under vacuum system and rather higher temperature (275 ℃) are required and the catalyst needs to be synthesized in much complex procedures.In contrast, the method reported in this work can be conducted in the air atmosphere, and requires much lower temperatures (＜160 ℃).Also, the catalyst we used in this method is cheap and easily commercially available.So, this method is much milder than the reported methods, making it more accessible to the high fluorinated CTF and also avoiding of damage by the high temperature to the chemical structure of the frameworks.
To make it more clearly, the Supplementary Table 1 and the corresponding discussion are added in the revised manuscript as follows: "The new synthetic approach enables the synthesis of perfluorinated CTF with high fluorine content and surface area under much milder conditions as compared to the reported methods (Supplementary Fig. 1 and Supplementary Table 1) 14,17-20 ." "Obviously, the fluorine content of CTF-TF is comparable to the highest values reported so far and is much higher than those of most fluorinated CTFs (Supplementary Table 1).
Notably, this marks the first instance of synthesizing a type of perfluorinated CTF with a significantly high fluorine content through such gentle methods.Previous conventional approaches struggled to achieve this level of perfluorination under mild conditions." [2] The authors should also compare the proton conductivity of their CTF-TF with other fluorinated CTFs that have been reported in the references.This would show how significant their improvement in proton conductivity is compared to previous studies.
Response: Thank you for your valuable suggestion.Recently, CTF materials have emerged as a promising platform for high temperature proton conduction applications.However, to the best of our knowledge, there is no report using fluorinated CTFs for the proton conduction at high temperatures so far.Thus, this work reports the first example of fluorinated CTFs applied to proton conduction at high temperature.
To directly compare with other methods, we thereby prepared a F-CTF-CN sample via conventional ionothermal strategy at 400 °C according to the literature method (Energy Environ.Sci. 2013, 6, 3684-369).It is found that the surface area of the F-CTF-CN (546.7 m 2 g -1 ) is higher than this method, but the fluorine content (11.76 wt%) is much lower than the CTF-TF (30.2wt%) of this work, which is due to the cleavage of the C-F bond at high temperature.After loading with phosphoric acid (50%), the proton conductivity of H3PO4@F-CTF-CN was tested to be only 6.64×10 −2 S cm −1 at 150 °C, which is much lower than that of H3PO4@CTF-TF (1.82×10 −1 S cm −1 at 150 °C).These results clearly indicate the present method can benefit for obtaining high fluorine content CTF and significantly increase the proton conductivity.
To make it more clearly, the corresponding discussion, supplementary figures and references have been added into the revised manuscript as follows: "For the purpose of further highlighting the advantages of our reported new method, F-CTF-CN was synthesized via ionothermal strategy, according to the related previous work 14 .

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[3] The authors have suggested that the strong interaction between CTFs and H3PO4 is important for achieving high proton conductivity.They have used XPS measurements to show that the incorporation of fluorine atoms into the CTFs enhanced the interaction between CTF-TF and H3PO4, leading to higher proton conductivity.However, they have not provided a clear correlation between the strength of the interaction and the proton conductivity for the three CTFs that they have synthesized.It is suggested that they quantify the interaction between CTFs and H3PO4 and provide a correlation between the interaction strength and the proton conductivity for each CTF.
Response: Thank you very much for the constructive suggestion.According to the Reviewer's comments, we analyzed the chemical structures of CTFs and conducted theoretical calculations to estimate the binding energies between CTFs and H3PO4, which may quantify the strength of interaction between them.
Firstly, the interaction between the CTFs and H3PO4 could be evaluated by the density of the interaction sites as hydrogen bond acceptors from the chemical structures of CTFs.In all the three CTFs, the triazine units are the major hydrogen bond acceptors to bind with H3PO4.
In addition to the triazine units, we can find that CTF-TF can provide abundant F atoms as additional hydrogen bond acceptors in the pores as compared to CTF-1.The large amount of F atoms renders CTF-TF comprise the largest density of interaction sites with protons in the framework among the three CTFs.The high density of hydrogen bond acceptors in the frameworks can benefit for the formation of hydrogen bonding networks, which facilitates the proton transport in the proton conduction.There are also two types of hydrogen bond acceptors in CTF-TPA, that are, N (triphenylamine) and N (triazine), however, the number of triazine N sites (major hydrogen bond acceptors) is only half of CTF-TF and CTF-1, making it inferior to form hydrogen bonding network and facilitate proton transport in proton conduction.
Secondly, according to the theoretical calculation results (as shown in Supplementary Fig. 14 and Supplementary Table 6), the CTF-TF displays a higher binding energy (-18.676kcal/mol) and lower proton dissociation enthalpy (4.481 eV) between the triazine N sites and phosphoric acid as compared to CTF-1 (-16.150kcal/mol and 4.543 eV), clearly indicating that the introducing of F atoms can indeed enhance the interaction between CTFs and phosphoric acid and facilitate the proton dissociation in the proton conduction simultaneously.Especially, the calculation shows that the interaction of phosphoric acid with F atoms has lower proton dissociation enthalpy (4.265 eV) as compared to the N atoms in the CTFs, which further facilitates the proton dissociation in the proton conduction.In the CTF-TPA, despite it exhibits higher binding energy of -22.347 kcal/mol on the N (triazine) sites than other CTFs, its halved N (triazine) hydrogen bond acceptors in CTF-TPA counteracts the positive effect on the proton conduction as compared to CTF-TF and CTF-1.
According to these analyses, we conclude that the introducing of F atoms can not only make the CTF-TF comprise the maximum number of hydrogen bond acceptors, but also benefit for the proton dissociation and transportation, thereby it effectively enhances the proton conductivity of CTF-TF, and that the overall strength of the interaction between the CTFs and phosphoric acid could be correlated with the proton conductivity performance.
To make it more clearly about the relationship and effect of fluorine atoms, the corresponding statement and discussion are added in the revised manuscript as follows: "Furthermore, the strength of the hydrogen bonding interactions can be probed by the values of binding energies from theoretical calculation.The H3PO4 molecules exhibit strong hydrogen bonding interaction when binding to the triazine nitrogen atoms of all three CTFs (Supplementary Fig. 14).Notably, getting benefit from the strong electron-withdrawing effect of fluorine, the nitrogen of triazine rings in CTF-TF exhibit stronger binding energy with H3PO4 as compared to that of CTF-1.In addition, as anchoring points, the fluorine atoms can not only provide more interaction sites, but also facilitate the proton dissociation between CTF-TF and Response: Thank you for this very insightful suggestion.To probe the impact of surface area and critical role of fluorine, we prepared a sample of CTF-TF-0.5 with lesser fluorine content by co-polymerizing, in which the amount of fluorine monomer decreased by 50%.The BET surface area of CTF-TF-0.5 (401.3 m 2 g -1 ) is very close to that of CTF-TF (407.7 m 2 g -1 ), but its fluorine content of 18.92 wt% is obviously smaller than CTF-TF (30.2wt%).It shows that the proton conductivity of H3PO4@CTF-TF-0.5 (1.22×10 −1 S cm −1 at 150 °C) is much lower than the CTF-TF (1.82×10 −1 S cm −1 at 150 °C) under the same conditions, clearly indicating that the fluorine is indeed crucial factor for enhancing the proton conductivity.The reason could be attributed to that the higher content of F atoms may act as hydrogen bond acceptor to stabilize the proton network and facilitate proton conduction.
[5] The authors should explain why there is no clear correlation between the activation energy and the proton conductivity for their CTFs.They have reported that H3PO4@CTF-1, H3PO4@CTF-TPA and H3PO4@CTF-TF have activation energies of 0.22, 0.10 and 0.37 eV, respectively, but their proton conductivities do not correlate with this order.They should provide some possible reasons for this discrepancy and discuss how it affects their interpretation of the results.
Response: Thank you for this insightful question.Indeed, there is no clear correlation between the activation energy and the proton conductivity in our experiments.Low activation energies are generally favorable for proton conduction.However, the proton conductivity is not solely related to the activation energy.The relationship between the temperature-dependent proton conductivity (σ) and the activation energy (Ea) follows the Arrhenius equation (Equation 1).
σ = σ0 exp(-Ea/kT) …… Equation 1where T is the temperature, σ0 is an experimental prefactor and k is the Boltzmann constant.
This means that the experimental prefactor (σ0) is also an important influencing factor.In the proton conduction, the experimental prefactor (σ0) and the activation energy (Ea) also have the following relationship, which is known as Meyer-Neldel rule (MNR) (Equation 2): lnσ0 = Ea/kTiso+ lnσ00……Equation 2 where σ00 and Tiso are constants, which depends on the proton conduction system itself.
The above equation shows that the change in prefactor compensates the change in activation energy.The conductivity variation of proton conductors follows the Meyer-Neldel rule, which is manifested as a compensation principle, that is, when the activation energy of proton conduction decreases, the prefactor in the conductivity formula will also decrease accordingly, resulting in a weakened optimization effect of the reduced activation energy on conductivity (Adv. Energy Mater., 2022, 12, 2102939).Thus, according to these principles, the proton conductivity and activity energy are not always correlated to each other clearly.
Furthermore, the factors that influence the proton conductivity can also be described in the following relationship (Nat. Mater. 2009, 8, 831-836;Chem. Mater. 2016, 28, 1489-1494): where n is the number of carriers, q is the charge, and μ is the mobility of the protons.
According to this relationship, the high activation energy may not be favorable for high mobility of the protons (μ), but it only partially affects the proton conduction to some extent.
Whereas, the number of the hydrogen bond acceptors in the CTFs could mainly determine the level of the proton conduction, which is due to that the more interaction sites between CTFs and phosphoric acid can not only result in higher number of proton carriers (n), but also form more hydrogen bonding networks to increase the mobility of the protons (μ).Further, the stronger interaction between the CTFs and phosphoric acid also facilitates the mobility of the protons (μ), benefiting for the proton conduction.As is the case in this work, the CTF-TF has the largest density of anchoring and interaction sites (F+N-triazine) with phosphoric acid than the CTF-1 and CTF-TPA, thereby leading to the highest proton conductivity.In contrast, even though the CTF-TPA has the lowest activation energy, the least density of effective hydrogen bond acceptors (triazine N sites) in the framework makes it exhibit the lowest proton conductivity.
The activation energy should be related to the proton transport pathways, which affects the energy barrier for proton conduction.We further probed the reason for the discrepancy of activation energy by experimental analysis and discussed the correlation with the proton conductivity.The corresponding statements and Supplementary Figures for discussion of the possible reasons for this discrepancy are added in the revised manuscript as follows: "The Ea is related to proton transfer pathways.However, it is found that the activation energies are not directly correlated to the proton conductivities.We performed the XPS measurements for the three H3PO4@CTFs and found that the high-resolution P 2p spectrums could be curve-fitted into two peaks at around 134.5 and 135.3 eV assigned to H2PO4 -and H3PO4, respectively 37,42 (Supplementary Fig. 13).The peak area ratios of H2PO4 − were calculated, which are in the order of H3PO4@CTF-TPA (62.4%) > H3PO4@CTF-1(61.0%)> H3PO4@CTF-TF (56.3%).Because the energy barriers for proton transfer pathways via H3PO4 →H2PO4 − is the lowest in H3PO4 loaded proton conducting polymers 43, 44 , the activation energy can be correlated to the H2PO4 − proportion.These results suggest that the higher the proportion of H2PO4 − , the lower the activation energy it may require for proton transfer." "The previous researches have shown that that the phosphate anion (H2PO4 -) dynamics favors the long-range proton transport 46,47   Response: Thank you for the insightful comments.Following the Reviewer's suggestion, we conducted the theoretical DFT calculation to probe the interaction between H3PO4 and CTFs.
According to the calculation results, the CTF-TF exhibits higher binding energy (-18.676kcal/mol) and lower proton dissociation energy (4.481 eV) on the N (triazine) sites as compared to CTF-1 (-16.150kcal/mol and 4.543 eV), indicating the introducing of F atoms can change the polarity of the framework and indeed enhance the interaction between the CTFs and H3PO4.
Especially, the calculation shows that the F atoms have much lower proton dissociation energy (4.265 eV) as compared to the N atoms in the CTFs series, which further facilitates the proton dissociation and transport in the proton conduction.As for CTF-TPA, as compared to CTF-TF and CTF-1, it exhibits a higher binding energy of -22.347 kcal/mol with H3PO4 on the N (triazine) sites, but a lower binding energy on triphenylamine N sites.Despite its higher binding energy on the N (triazine) sites, the number of N (triazine) sites is only half of that in CTF-TF and CTF-1, which counteracts the positive effect of binding energy on the proton conduction.
Thus, the introducing of F atoms can not only directly increase the density of hydrogen bond 13 / 37 acceptors for higher proton number, but also enhance the ability of proton dissociation and transport in the proton conduction process.
Moreover, to demonstrate the electronic structure and polarity of the CTFs, we drew the electrostatic potential (ESP) maps of CTFs, which shows that the presence of F atoms in CTF-TF renders its pores electronegative, as indicated by a highest ESP value of -0.533 eV.Proton transfer usually tends to occur between H3PO4 and H2PO4 − (J.Electrochem.Soc., 2004, 151, A8-A16; Int.J. Quantum. Chem., 2011, 111, 3212-3229).Therefore, phosphate anion (H2PO4 − ) dynamics is important to contribute to long-range proton transport (J.Phys.Chem. B, 2007, 111, 5602-5609;Chem. Soc. Rev., 2010, 39, 3210-3239).Due to the highest electronegativity, H2PO4 − dynamics would be accelerated by the electrostatic repulsion in CTF-TF to facilitate proton migration.Therefore, although the activation energy of H3PO4@CTF-TF is high, the other positive factors still make it show excellent proton conductivity.

The corresponding explanation with references and Figures about how fluorine atoms
enhance the proton conductivity is given in the revised manuscript as follows: "Furthermore, the strength of the hydrogen bonding interactions can be probed by the values of binding energies from theoretical calculation.The H3PO4 molecules exhibit strong hydrogen bonding interaction when binding to the triazine nitrogen atoms of all three CTFs (Supplementary Fig. 14).Notably, getting benefit from the strong electron-withdrawing effect of fluorine, the nitrogen of triazine rings in CTF-TF exhibit stronger binding energy with H3PO4 as compared to that of CTF-1.In addition, as anchoring points, the fluorine atoms can not only provide more interaction sites, but also facilitate the proton dissociation between CTF-TF and H3PO4 due to F•••H−O hydrogen bonds.The binding energy of triazine nitrogen to H3PO4 in CTF-TPA is the highest among them, but the amount of triazine nitrogen acceptors in the framework structures is halved as compared to that of CTF-1 and CTF-TF.Overall, the CTF-TF gives the highest strength of interaction with phosphoric acid among the three CTFs.The additional host-guest interaction sites given by F benefits for the phosphoric acid confinement and proton dissociation in the channels of CTF-TF, leading to better proton conductivity among the series." "The previous researches have shown that the phosphate anion (H2PO4 -) dynamics favors the long-range proton transport 46,47 .As depicted in Supplementary Fig. 15,  adopts a non-planar structure due to the incorporation of triphenylamine units, and an electronegative region is also observed at the N atoms of the triazine moieties.Consequently, CTF-TF exhibits a pronounced electron-withdrawing capacity within its pores, while CTF-1 displays the opposite behavior.CTF-TPA, on the other hand, exhibits electron-withdrawing or electron-donating capabilities at different positions within its pores, depending on the local environment.H2PO4 − dynamics that benefit for the proton conduction would be accelerated in CTF-TF due to electrostatic repulsion, while it may be inhibited in CTF-1 and CTF-TPA.
Therefore, although the activation energy of H3PO4@CTF-TF is high, the other positive factors still make it result in excellent proton conductivity." Supplementary Table 6.Summary of the binding energy and proton dissociation energy results of the theoretical calculation (PA:H3PO4).Response: Thank you so much for your great efforts in reviewing our revised manuscript.We sincerely appreciate your valuable comments and suggestions, which have certainly helped us to improve the quality of this manuscript.The manuscript was carefully revised based on these suggestions.Additional experiments and theoretical results were performed to provide solid supports in the revision.We look forward to your positive support for our revised manuscript.
To further strengthen the novelty and significance of our work, we explain them again in the following aspects: ( (2) New Findings about the Effect of Fluorine in High Temperature Proton Conduction Most of the works have studied the effect of some heteroatoms, such as nitrogen, in the proton conduction at high temperatures, but the effects of other special atoms have been rarely explored.Herein, we for the first time demonstrate that the fluorinated CTFs are promising for high temperature proton conduction.We show that the perfluorinated CTF endowed by the high fluorine content can provide as many anchoring sites as possible to interact with proton carriers and facilitate the proton transport.We further use DFT to investigate the host-guest interactions between H3PO4 and CTFs at a molecular level and revealed that the introducing of F atoms can not only directly increase the number of hydrogen bond acceptors for protons number, but also enhance the ability of proton dissociation and transport in the proton conduction process.
As above, the novel synthesis method for CTFs we have shown here, and the interesting effect of fluorine in the excellent proton conduction performance we revealed in this work, have not been reported in other works.Thus, we believe that this work shows sufficient novelty and advantage as compared to the reported references, which would be enlightening for the wide readership and thereby deserve to be published in Nature Communications.
To further clarify the novelty and advantage in this work, the manuscript has been thoughtfully revised, which is marked in the revision and summarized as followings.

✓ Reorganization of Introduction section
In the revision, the Introduction section is revised.The novelty and advantage of this new method are emphasized.
"The regulation of CTFs in proton conduction at high temperatures are mainly focused on heterocyclic nitrogen and aromatic structures.To enhance the proton conductivity, it is important to introduce as more hydrogen bond acceptors as possible, which may increase the host-guest interaction with the CTFs and proton carriers.However, due to the limitation of synthesis methods and the building blocks, the introduction of other precise hydrogen bond acceptors as active sites to increase the host-guest interaction in CTFs for proton conduction has not been widely explored." "While in CTFs, the introduction of fluorine atoms may greatly benefit for high temperature proton conduction because it may increase the host-guest interaction between the CTF and the proton carriers.In particular, perfluorinated CTFs with high fluorine content could exhibit the greatest number of anchoring sites with proton carriers in the framework structures." "Herein, we successfully established a new approach to synthesize CTFs via direct cyclotrimerization of aromatic aldehydes using NH4I as facile nitrogen source for the first time (Fig. 1).The conditions of this method are much milder, using low temperature (160 ℃), openair atmosphere, readily available raw materials, and relatively low catalyst dosage.We have found that the gentle approach is highly effective to synthesize CTFs with various structures.
Particularly, the new synthetic approach enables the synthesis of perfluorinated CTF with high fluorine content and surface area under much milder conditions as compared to the reported methods (Supplementary Fig. 1 and Supplementary Table 1) 14,17-20.The resulting CTFs display promising proton conduction properties after binding with the H3PO4 with the merits of rich nitrogen content and high stability 6-9 .In particular, the electronegative fluorine sites together with the triazine units in the perfluorinated CTF (CTF-TF), which provide the precise host-guest interaction sites, can effectively lock H3PO4 and act as hydrogen bond acceptor to facilitate proton transport.Consequently, the CTF-TF loading with H3PO4 delivers an excellent proton conductivity of 1.82 × 10 −1 S cm −1 at 150 °C, which ranks the highest value among the reported CTFs and is also comparable to other excellent porous organic polymer conductors.To the best of our knowledge, it is the first example to endow fluorinated CTF with high proton conduction by this work.Thus, this work provides a new powerful way to extend the functionality and applications of the CTFs."

✓ More results on mechanism of how fluorine atoms enhance the proton conductivity
In the revision, DFT calculation was used to investigate the interaction between H3PO4 being close to the sites.Considering the amount of hydrogen bond acceptors (N) in the frameworks, the overall strength of the interaction between the CTF-TPA skeleton and H3PO4 should be smaller than CTF-1.The isosurfaces reveal the presence of extensive intermolecular interactions between the hydrogen donors (H3PO4) and acceptors (F atoms) in H3PO4@CTF-TF, indicating a strong interaction between H3PO4 and CTF-TF, when H3PO4 is inside the pore.
"The previous researches have shown that the phosphate anion (H2PO4 -) dynamics favors the long-range proton transport 46,47 .As depicted in Supplementary Fig. 15, the electrostatic potentials (ESP) of the three CTFs exhibit distinct variations.The presence of fluorine (F) atoms in CTF-TF renders its pores electronegative, as indicated by a maximum ESP value of -0.533 eV.Conversely, the pores of CTF-1 exhibit electropositive characteristics, with an [1] The impedance measurements lack information about the relative humidity.Proton conductivity is known to be strongly dependent on humidity, including in organic polymers such as these.A careful control over and systematic variation of humidity would be mandatory to assess how much the conductivity is mediated by water.
Response: Thank you very much for the insightful comments.The control of humidity is indeed important in the low temperature (< 100 °C ) proton conduction system, because the proton conductivity is mainly affected by the humidity at low temperature.Thus, the proton conduction under controlled humidity should be studied at lower temperatures (＜100 °C).Your suggestion is an important research topic and provides a direction for our next research.
However, in this study, what we investigated is the proton conductivity at higher temperatures (>100 °C , higher than the boiling point of water), which is different from the low temperature proton conduction systems.The high-temperature proton conduction employs high-boiling point proton carriers, i.e.H3P3O4, which avoids the presence of water and thereby simplifies the water and heat management (J. Power Sources, 2013, 231, 264-278).With an aim to develop efficient proton conductive materials at high temperatures, we report in this work a new synthetic route for CTF-TF under mild conditions and explore the effect of fluorine atoms in the high-temperature proton conductivity.Therefore, all the samples we have used have been efficiently vacuumed dried at high temperatures (150 °C ) to efficiently remove the residual water before the measurement.And, the proton conductivity by EIS in our study was conducted under the anhydrous condition.
With all due respect, our experiments however have ultimately avoided the presence of water in the measurements, which makes it not accessible to control the humidity at high temperatures.According to the literatures, all the related reports have not investigated the controlled humidity in the high temperature proton conduction measurements (Nat. Mater. 2016, 15, 722-726;Adv. Energy Mater. 2021, 39, 2102300;Nat. Commun. 2020, 11, 1981).Therefore, in this work the proton conductivity under controlled humidity at high temperatures (100~160 °C ) is also not shown.We hope you could understand our situation.
For the clear understanding of the measurement condition, the related description of the measurement condition has been stated in the previous manuscript (proton conductivity measurement section in supplementary text): "The proton conductivity (σ, S cm -1 ) of CTFs-H3PO4 were characterized by EIS under the anhydrous condition." 23 / 37 [2] What does "semi-crystalline" mean (XRD)?The term needs explanation.In addition, a peak in the XRD diagram (Suppl.fig.5) at ca. 18° is not explained, either.
Response: Thank you for professional question."Semi-crystalline" means that the materials comprise of both crystalline and amorphous regions (PNAS 2023, 120, e2217363120).In order to avoid confusion for the readers, we have revised the description in revised manuscript.
[3] The interpretation of the N2 physisorption analysis is questionable.Hysteresis closure at ca. P/P0 = 0.42 is most likely due to network effects ('forced hysteresis closure', 'tensile strength effect') rather than caused by mesoporosity.

Response:
We appreciate this insightful comment.We completely agree with your professional comments.The hysteresis is usually attributed to the thermodynamic or network effects or the combination of these two effects (Chem. Mater. 2001, 13, 3169-3183).H4 hysteresis loops may merely arise from the presence of large mesopores embedded in a matrix with pores of much smaller size.
To address the Reviewer's concern, we have revised this part as follows: "And it features a typical type H4 hysteresis loop, which is most likely attributed to network effects, due to the presence of mesoporous and microporous structures together 35 ." 35.Kruk, M. Jaroniec, M. Gas adsorption characterization of ordered organic−inorganic nanocomposite materials.Chem.Mater. 13, 3169-3183 (2001).
[4] According to the TGA data, the materials not really seem to be stable at temperature above ca.150 °C.
Response: Thank you for your insightful comment.In order to clearly show the variation of CTFs at 100 ~ 200 °C, the TGA curve was locally enlarged (See graph below), and the results showed that CTFs could be stable at 150 °C without loss of mass.When the temperature further reach 200 ℃, there is still only a negligible amount of mass loss in CTFs.The further weight loss at higher temperatures is also very normal, which could be due to the decomposition of some remaining or peripheral groups.Such phenomenon is widely observed for CTFs and other COFs as reported in the literatures (See figures below).

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The partially enlarged TGA curves shows the CTF-TPA only has slight weight loss up to 200 °C.
These are the TGA patterns of CTFs and other COFs reported by the previous literatures.As you may see that all of them showed some mass loss from 200 °C.

Responses to Reviewer #3:
[Remarks to the Author]: The manuscript by S. Jin and workers describes the low-temperature synthesis of covalent triazine frameworks and investigation of their proton conductivities.The synthesis approach is a good alternative to those reported procedures and the proton conducting performances of the obtained CTFs are high.I would like to recommend acceptance for publication after addressing the following points.

Response:
We appreciate the reviewer for the insightful comments and positive evaluation.
[1] The authors should emphasize the novelty and advantage of the NH4I-involved procedure and provide the comparison with other processes.

Response:
We appreciate this comment.Following your suggestion, we emphasize the novelty and advantage of this work as follows: Recently, CTF materials have emerged as a promising platform for high temperature proton conduction applications.To enhance the proton conductivity, it is highly desired to further increase the hydrogen bond acceptor sites and host-guest interaction with proton carriers.
Also, to achieve excellent proton conductivity, it is important to retain intact of the chemical structure during synthesis and high content of the hydrogen bond acceptors in the framework, so it is strongly anticipated to synthesize the materials at lower temperatures.Traditionally, fluorinated organic polymers, exemplified by NAFIONs, play a pivotal role in achieving high conductivity and stability.Consequently, it becomes paramount to enhance the fluorine content within CTF materials.
In this study, we introduce a novel approach to synthesize Covalent Triazine Frameworks (CTFs) through the direct cyclotrimerization of aromatic aldehydes, employing NH4I as a readily available nitrogen source under mild conditions.Notably, this marks the first instance of synthesizing a type of perfluorinated CTF with a significantly high fluorine content through such gentle methods.Previous conventional approaches struggled to achieve this level of perfluorination under mild conditions.Thus, it is of great importance to develop new method to construct CTFs with versatile structures under milder conditions.
We compare this method to other reported ones and highlight that the starting materials and the reagents in this method are all commercially available.The conditions of this method are quite mild, using low temperature (＜160 ℃), readily available raw materials, and relatively lower catalyst dosage.Based on this novel cyclotrimerization method, a highly fluorinated CTF (CTF-TF) can be successfully achieved under mild conditions as compared to previous methods.
With this strategy, it is also potential to develop new and special functions for CTFs.
In the revision, the corresponding discussion to emphasize the novelty and advantage of this work in the Introduction section was revised as follows: "The regulation of CTFs in proton conduction at high temperatures are mainly focused on heterocyclic nitrogen and aromatic structures.To enhance the proton conductivity, it is highly desired to introduce as more hydrogen bond acceptors as possible, which may increase the hostguest interaction with the CTFs and proton carriers.However, due to the limitation of synthesis methods and the building blocks, the introduction of other precise hydrogen bond acceptors as active sites to increase the host-guest interaction in CTFs for proton conduction has not been widely explored." "While in CTFs, the introduction of fluorine atoms may greatly benefit for high temperature proton conduction because it may increase the host-guest interaction between the CTF and the proton carriers.In particular, perfluorinated CTFs with high fluorine content could exhibit the greatest number of anchoring sites with proton carriers in the framework structures." "Herein, we successfully established a new approach to synthesize CTFs via direct cyclotrimerization of aromatic aldehydes using NH4I as facile nitrogen source for the first time (Fig. 1).The conditions of this method are much milder, using low temperature (160 ℃), openair atmosphere, readily available raw materials, and relatively low catalyst dosage.We have found that the gentle approach is highly effective to synthesize CTFs with various structures.
Particularly, the new synthetic approach enables the synthesis of perfluorinated CTF with high fluorine content and surface area under much milder conditions as compared to the reported methods (Supplementary Fig. 1 and Supplementary Table 1) 14,17-20 " [2] The proton conductivity results should be explained considering the chemical structures.

Response:
We thank the constructive suggestion.By considering the chemical structures of CTFs, we have used DFT calculation to probe the interaction between H3PO4 and CTFs, to provide more insights into the role of fluorine atoms in modifying the electronic structure of the CTFs and discuss the mechanism of how fluorine atoms enhance the proton conductivity.
Moreover, we constructed CTF-TF-0.5 with different contents of F atoms as control sample to prove that the high density of H-bond acceptors facilitates the formation of a proton transport pathway and thus improves the proton conductivity.
Firstly, to show the relationship of the chemical structures with the proton conductivity, the calculation of the binding energies between H3PO4 and CTFs at a molecular level using DFT was conducted.Due to the strong hydrogen bond between F and phosphoric acid, CTF-TF has the highest overall strength of interaction and the largest hydrogen bond acceptor density, which are beneficial to a high proton conductivity.According to the calculation results based on the different chemical structures, the CTF-TF exhibits higher binding energy (-18.676kcal/mol) and lower proton dissociation energy (4.481 eV) on the N (triazine) sites as compared to CTF-1 (-16.150kcal/mol and 4.543 eV), indicating the introducing of F atoms can change the polarity of the framework and indeed enhance the interaction between the CTFs and H3PO4.
Especially, the calculation shows that the F atoms have much lower proton dissociation energy (4.265 eV) as compared to the N atoms in the CTFs series, which further facilitates the proton dissociation and transport in the proton conduction.As for CTF-TPA, as compared to CTF-TF and CTF-1, it exhibits a higher binding energy of -22.347 kcal/mol with H3PO4 on the N (triazine) sites, but a lower binding energy on triphenylamine N sites.Despite its higher binding energy on the N (triazine) sites, the number of N (triazine) sites is only half of that in CTF-TF and CTF-1, which counteracts the positive effect of binding energy on the proton conduction.

[ 4 ]
H3PO4 due to F•••H−O hydrogen bonds.The binding energy of triazine nitrogen to H3PO4 in CTF-TPA is the highest among them, but the amount of triazine nitrogen acceptors in the framework structures is halved as compared to that of CTF-1 and CTF-TF.Overall, the CTF-TF gives the highest strength of interaction with phosphoric acid among the three CTFs.The additional host-guest interaction sites given by F benefits for the phosphoric acid confinement and proton dissociation in the channels of CTF-TF, leading to better proton conductivity among the series."Supplementary Fig. 14.Graphic representations of the binding energy of H3PO4 to various interaction sites for CTFs.(a) CTF-1(Triazine N), (b) CTF-TPA (Triazine N), (c) CTF-TPA (Triphenylamine N), (d) CTF-TF (F) and (e) CTF-TF (Triazine N). (H, white; P, brown; O, red; N, blue; C, cyan; F, LT Magenta).Summary of the binding energy and proton dissociation enthalpy results of the theoretical calculation (PA:H3PO4).The authors should also consider the effect of BET surface area on the proton conductivity of their CTFs.The three CTFs that they have synthesized have different BET surface areas, which may influence their proton conductivity.The authors should either normalize their proton conductivity data to the BET surface area or use CTFs with similar surface areas to exclude this effect and demonstrate that fluorine incorporation is indeed responsible for enhancing the proton conductivity.

[ 6 ]
It is suggested that the authors use DFT or FTIR to investigate the interaction between H3PO4 and CTFs at a molecular level and further elucidate the mechanism of how fluorine atoms enhance the proton conductivity.This would provide more insight into the role of fluorine atoms in modifying the electronic structure and polarity of the CTFs and how they affect the mobility and transfer of protons.
the electrostatic potentials (ESP) of the three CTFs exhibit distinct variations.The presence of fluorine (F) atoms in CTF-TF renders its pores electronegative, as indicated by a maximum ESP value of -0.533 eV.Conversely, the pores of CTF-1 exhibit electropositive characteristics, with an electronegative region observed near the nitrogen atoms of the triazine moieties.CTF-TPA 14 / 37 Graphic representations of the binding energy of H3PO4 to various interaction sites for CTFs.(a) CTF-1(Triazine N), (b) CTF-TPA (Triazine N), (c) CTF-TPA (Triphenylamine N), (d) CTF-TF (F) and (e) CTF-TF (Triazine N). (H, white; P, brown; O, red; 15 / 37 N, blue; C, cyan; F, LT Magenta).46.Traer, J. W., Britten, J. F. & Goward, G. R. A solid-state NMR study of hydrogenbonding networks and ion dynamics in benzimidazole salts.J. Phys.Chem.B 111, 5602-5609 (2007).47.Asensio, J. A., Sánchez, E. M. & Gómez-Romero, P. Proton-conducting membranes based on benzimidazole polymers for high-temperature PEM fuel cells.A chemical quest.Chem.Soc.Rev. 39, 3210-3239 (2010).Supplementary Fig. 15.Electrostatic potential of (a) CTF-1, (b) CTF-TPA, and (c) CTF-TF.Responses to Reviewer #2: [Remarks to the Author]: Guan et al. present an interesting paper on the synthesis of fluorinated triazine framework that show good proton conductivity when impregnated with phosphoric acid.The work may generally be publishable but lacks the high degree of novelty and significance needed for Nature Communications.In addition, several issues are unclear (see below).Therefore, I do not recommend publication in this journal.

Table 1 .
Comparison of previous reported fluorinated CTFs prepared by different methods with this work.

1) A New Method to Synthesize CTFs at Mild Conditions
to enhance the fluorine content within CTF materials.In this study, we introduce a novel approach to synthesize Covalent Triazine Frameworks (CTFs) through the direct cyclotrimerization of aromatic aldehydes, employing NH4I as a readily available nitrogen source under mild conditions.Notably, this marks the first instance of synthesizing a type of perfluorinated CTF with a significantly high fluorine content through such gentle methods.Previous conventional approaches struggled to achieve this level of perfluorination under mild conditions.Thus, it is of great importance to develop new methods for CTFs with versatile structures, and this method provides a new avenue to create such functional CTFs.It is worth emphasizing that the starting materials and reagents used in this method are readily accessible, and the reaction conditions are notably mild, characterized by low temperatures (below 160 ℃) and a relatively modest catalyst dosage.
temperatures.Recently, CTF materials have emerged as a promising platform for such applications.Traditionally, fluorinated organic polymers, exemplified by NAFIONs, play a pivotal role in achieving high conductivity and stability.Consequently, it becomes paramount 16 / 37